Torque converter

A hydrodynamic torque converter or Föttinger converter is a hydrodynamic transmission. It was originally developed by the engineer Hermann Föttinger for marine propulsion, and later also used in motor vehicles and locomotives.

In vehicles with automatic transmission, the special Trilok converter is used as a starting today usually. The peculiarity of Trilok converter is that when starting with high input speed and low drive torque at output high torque is produced at low or no speed. The change from high torque output at low output speed to low output torque at high output speed is infinitely variable and automatically at constant engine power. The conversion range is now at up to 1:3 ( the severance torque remains three times the input torque).

In general, each transmission may be a torque converter in relation to the applied torque.

History

Trilok converter and have been known since the early 20th century:

In the following years numerous refinements are introduced to the market, such as converter lockup clutches, simplified production by sheet metal forming, integration of torsional dampers and dual mass flywheels.

Technology

Demarcation

The torque converter is based on the Föttinger clutch. The Föttinger coupling has only pump and turbine, so that between input and output a speed difference may be present, input and output torque remain the same, so there is no conversion of the torque.

Operation

A torque converter is made in the simplest case of the components impeller, turbine and guide wheel, which are installed in a common oil-tight housing. The principle of hydrodynamic power transmission is that a liquid ( oil, water, oA ) is captured and accelerated by the blades of the impeller. The impeller, which is driven directly from the engine, converts the mechanical energy to flow energy, it forms the so-called primary side. The turbine wheel is directly connected to the transmission output shaft for pure hydrodynamic transmissions ( secondary side ), this energy flow resumes and provides mechanical energy available at the output of the converter. The stator is rigidly connected to the housing and can not rotate. The oil is supported on the curved by about 90 degrees of the stator blades, thereby causing a strong back pressure, which results in an increase of the torque the effect on the blades of the turbine wheel. Characterized the torque on the turbine shaft ( output shaft ) is larger than the gas introduced into the torque converter torque motor. Simultaneously, the reaction member ( stator ) undergoes a corresponding torque which must be supported. The stator is necessary as a torque support, otherwise there can be no torque conversion and only the function of a pure coupling would be achieved. Furthermore passes the stator the oil flow at a favorable angle back on the blades of the impeller so that the oil circuit is self-contained. The transmitted power is out of the interpretation of the transducer depends only on the speed and increases with this on.

The torque change is dependent on the rotational speed difference between the pump and turbine. The greater the difference, the greater can be the excessive torque. When adjust both speeds, decrease from the efficiency and the torque overshoot of the converter. There are several approaches to still achieve a consistently high efficiency: In large gears usually several hydraulic circuits for different speed ranges are used which are automatically filled or emptied according.

Trilok converter

In so-called converter Trilok the stator is mounted on a free wheel, so that the converter for pure hydrodynamic coupling ( coupling portion ) can be changed; the stator rotates after switching freely.

In contrast to simple hydrodynamic couplings, which were once used under the name " Föttinger clutch " in automatic transmissions, you can see a torque converter and a Trilok converter in mind that in addition to the driving and driven even a torque arm, for example as attachment to the housing, is required.

Newer automatic transmissions is a lockup clutch ( torque converter lockup clutch, short VCCR ) was used. This connects the pump directly to the turbine. Thus, a direct mechanical connection between the input and output side is a, which corresponds to an efficiency of nearly 100%. However, as also in Trilok converter is after the changeover, no torque change instead.

The converter also dampens torsional vibrations in the drive train, so that suggestions of the engine are not transmitted to the body through the cardan and drive shafts.

Installation in vehicles

The torque converter is typically used in automotive and Baumaschinenbau in automatic transmissions and connecting the crankshaft with the further parts of the automatic transmission. The locomotive and shipbuilding pure hydrodynamic transmission are often used which contain a plurality of torque converter or hydraulic couplings.

Since the efficiency of a torque converter rarely exceeds 85% and in the coupling area of a Trilok converter is approximately 95%, a considerable part of the transmission input power is converted into heat, which must be dissipated. Therefore, a part of the working fluid is continuously held and cooled in the circulation. The use of a torque converter lockup clutch reduces losses considerably. Often, the clutch is used already in the low gears and the torque converter largely limited to its function as a start. During start-up offers a Trilok converter thanks moment cant even a higher efficiency than a conventional abrasive clutch. Car with perfect designed automatic transmissions and torque converters can often accelerate faster than same manually shifted thanks to the torque peaks of Trilok converter.

With the bridging of the torque converter, the efficiency improved, but also the vibration damping effect is eliminated, since the power transmission takes place via the mechanical force closing and no longer through the hydraulic fluid. In order to meet the comfort requirements here called Turbinentorsionsdämpfer (TTD ) may be used. Another way to minimize this disadvantage, is to not completely close the lockup clutch, but also to operate with a load - and speed-dependent slip speed. However, the resulting in the friction elements of the lockup clutch heat must also be removed via a properly sized, continuous exchange of the liquid in the transducer.